Method and means for reducing electrical disturbances



D. G. M CAA Feb. 18, 1936.

METHOD AND MEANS FOR REDUCING ELECTRICAL DISTURBANCES Fiied Jan. 22, 1950 2 Sheets-Sheet 1 O FDl F301 0 I 710612739 David 6. 7770.

fl'O/"Iw [a I D. G. M CAA 2,031,539

METHOD AND MEANS FOR REDUCING ELECTRICAL DISTURBANCES Feb. 18, 1936.

Filed Janj 22, 1930 2 Sheets-Sheet 2 Im i740 i1 6. me. (Jan,

Patented Feb. 18, 1936 2,031,539

UNITED STATES PATENT OFFICE METHOD AND MEANS FOR REDUCING ELECTRICAL DISTURBANCES David G. Mccaa, Philadelphia, Pa.

Application January 22, 1930, Serial No. 422,617

18 Claims. (01. 250-20) This invention relates to improvements in Another object is the provision of suitable methods and means for reducing the effects of plate voltages for the rectifying tube from which electrical disturbances and particularly refers to the biasing voltage is derived so that the plate reducing electrical disturbances in radio receivvoltage is always of sufiicient value to function ing systems which may be present in the form with the grid bias on the rectifier to give sub- 5 of electrostatic-discharges from the atmosphere stantially zero plate current when no signals are known as static, or artificial electrical noises. present. These plate voltages are also provided The invention is, of course, applicable to transautomatically in accordance with the carrier mission along telephone lines where the disturbsignal volta ances may be in the form of line surges or any A further object is to provide means for auto- 10 other line noises which would tend to predomimatically biasing the rectifier tube in accordance nate over the signaling currents. The general with the incoming carrier voltage. principles of this application are disclosed in A still further object of the nvention is to co-pending application, Serial No. 74,087, filed provide means for preventing the building up of Dec. 8, 1925, upon which Patent No. 1,814,051 excessive biasing voltage on the grid of the vac- 15 has been granted. The present invention is in uum tube of .a circuit which may be caused by the nature of an improvement on that of the excessively high input voltages and thereby preearlier application. venting the blocking of the tube.

One of the objects of the invention is to pro- Other objects and advantages will appear vide means which will prevent the transmission hereinafter. 20 of the disturbances to the output of a receiving The nature and objects of the invention will system, the means depending for operation on be better understood from the following detailed the biasing principle, that is, said means being description together with the drawings, in rendered effective by a biasing voltage applied which: thereto which is of a value comparable with the Fig. l is a basic diagrammatic circuit showing 25 peak signal voltage. the automatic biasing of a two-element ther- Another object is to provide means for obtainmionic vacuum tube in accordance with signal ing the biasing voltage automatically from the voltages; receiving system so that it will always be of a Fig. 2 is a modification showing two threevalue comparable with the peak signal voltage, element thermionic vacuum tubes which are 30 that is, if the signal voltage increases, the biasautomatically biased in accordance with signal ing voltage will be automatically adjusted to the voltages from the output of a detector tube required value. which may be operated at substantially zero Another object is to provide means in the form plate current when no signals are present; of a balanced impedance network or Wheatstone Fig. 3 is a wiring diagram of a balanced net- 35 bridge including a variable impedance for renwork or Wheatstone bridge modified in accorddering the electrical disturbances ineifective on ance with my invention to prevent electrical disthe signal output. The impedance network or turbances passing therethrough; and

Wheatstone bridge is normally unbalanced when Fig, 4 is a wiring diagram of a complete re- 0 disturb-311685 are present and the Signal curceiving system embodying my improvements and 40 rent is Permitted to flow therethroug 1111- shcwing the use of the balancing network or afiwted- As soon as disturbances of higher Volt Wheatstone bridge and also the connections for age are present, the impedance network or obtaining automatic biasing voltages for the tubes Wheatstone bridge becomes automatically less in the bridge and for the rectifier from which unbalanced to the high amplitude voltages due the bridge bias is obtained 5 to variation of value of the variable impedance Referring to Fig. 1, v represents a ode a and cathode and coupled to the input of the network. f d Another object is to provide a biasing voltage pnmary 601 P by means 0 sewn ary In to be applied to the variable impedance device, series with the anode and cathode is inserted a the value of which depends on the output signals. time Circuit Comprising a Sta Ge R shunted Another object is to provide means for prey COIldBnSeI A battery B W its aventing the disturbing oscillations from generattive terminal connected through the secondary S 65 ing biasing voltages. to the anode a is provided toprevent normal emission current from flowing from the anode to the cathode of tube V.

The operation of the system shown in this figure is as follows:When there are no signals present, the tube V is held open or, in other words, the circuit of secondary S is held opencircuited because of the battery B which should be of such a value as to prevent normal emission current from flowing from anode to cathode. By means of the time circuit RC, the tube is held open in accordance with the envelope of the signals, that is, when signals are present, a current begins to flow in the circuit of secondary S and this current produces a voltage drop across the resistance R which causes a more negative voltage to be impressed on the anode, thereby blocking the tube and causing the circuit to become open again. The elements of the time circuit RC are of such value that a predetermined length of time is required for a voltage to build up therein so that signal oscillations which are of a. much longer duration thandisturbing oscillations render the time circuit effective while the disturbing oscillations such as static surges are of a comparatively short duration cannot build up a voltage therein and. therefore, do not bias the tube.

In Fig.- 2 is shown a wiring diagram illustrating the application of the automatic bias voltages produced by the time circuit RC to a system for reducing the effects of electrical disturbances on signal oscillations. The system is of the type described in my co-pending application, Serial No. 383,932, filed Aug. 6, 1929. The automatic bias system of the present invention is substituted for the fixed bias used in the co-pending application. The diagram shows a pair of input terminals 1 and 2 connected to a pair of primary coils P1 and P2 which are in series. P1 and P2 are inductively coupled in opposed relation to S3 and-independently inductively coupled to secondaries S1 and S2, respectively. In the circuit of S1 are connected in parallel a pair of tubes V and V1, in the plate circuits of which may be a source of potential B1. This source of potential is provided to prevent normal emission current from flowing. The grid-filament circuits of the two tubes are connected across the time circuit RC, which is in the anode-cathode circuit of the detector tube V2. The anode of the detector tube V2 is energized by the DC source of potential B2. A filter comprising a suitable choke coil and a condenser C1 is provided to prevent any sudden surges being impressed on the time circuit RC. The detector in the present instance may be of the type in which the normal plate current is substantially zero. The input for the detector V2 is provided from the output secondary S3. The secondary S2 is connected in series with an adjustable resistance R2. The resistance R2 is so adjusted as to balance the impedance of the circuit of the secondary S1 only when the tubes are conducting. The entire circuit corresponds to a Wheatstone bridge arrangement in which the primaries P1 and P2 are analogous to the equal fixed resistances of one arm of the bridge and the circuits of S1 and S2 are analogous to the adjustable balancing resistances of the other arm of the bridge. When signals are present in the primaries P1 and P2, the circuit of the secondary S1 isnon-conductive because of the bias impressed on the grids of the tubes V and V1 from the time circuit RC which is obtained by the voltage drop produced by the plate current games from the detector tube V2. The circuit of the secondary S2, however, is conductive and the energy from the primary P2 is diverted thereto, causing an unbalance between the fields of primaries P1 and P2, thereby effecting a transfer of signal voltages from the primary P1 to the secondary S3. As the strength of the incoming signal oscillations increases or, in other words, as the amplitude increases, the plate current in the detector tube V2 increases, thereby producing a greater drop across the resistance R and applying a greater negative bias on the tubes V and V1 to maintain the circuit of the secondary S1 non-conductive. Thus, it will be seen that the tubes V and V1 are automatical'ly biased in accordance with the signal amplitude and the circuit of the secondary S1 is always maintained non-conductive regardless of the value of the peak signal voltage of the incoming oscillations. Undesired oscillations coming in through primaries P1 and P2 do not affeet the bias on the tubes V and V1, because the duration of the undesired oscillations is comparatively short and they, therefore, cannot cause the time circuit RC to function since it requires a predetermined length of time to actuate it. As in the case of Fig. l, the disturbing oscillations such as static surges or line surges lack the time to build up a substantial voltage across the time circuit RC. The peak voltages, however, of the undesired oscillations are sufficiently great to overcome the impedance of the circuit of S1 and are diverted thereto as well as to the circuit S2, thereby producing a balance between P1 and P2 and preventing any of the undesired oscillations from being transferred to the output secondary S3.

The operation of the system of Fig. 2 is further enhanced by the-fact that the arrangement of the primaries P1 and P2 in opposed relation provides a substantially balanced supply for the disturbing oscillations so that their effects are neutralized and cannot be effectively transferred to secondary S3. However, if there be a slight leakage of the disturbing oscillations to the secondary, they lack the energy and time, as explained hereinbefore, to build up a voltage across RC and, therefore, do not produce a bias on the tubes V1 and V2.

In Fig. 3 is shown a balancing network or Wheatstone bridge in which one of the resistances is replaced by a pair of two-element rectifiers which are adjusted by biasing to allow only high amplitude voltages to pass, but to block signal voltages. The bias on these two tubes is provided automatically from the system in which the bridge is located so that when the peak signal voltage increases, a corresponding increase in the biasing voltage will take place. The resistances R1 and R2 are fixed and may be equal. The resistance R3 is variable andmay be adjusted so that it will be equal to the total resistance of the tubes V and V1. Condensers C3 and C4 are provided across the resistance R5 to by-pass alternating current voltages which may leak through from the biasing system and prevent their generating a bias on the tubes V and V1. The condensers C3 and C4 in combination with R5 also constitute a time circuit which functions to prevent the disturbing voltage such as static surges and the like from over-biasing the tubes. When condensers C3 and C4 are not used, alternating current must fiow through one-half of the resistance R5 andthe valve in series therewith and the balance point on the adjustable resistance R: shows that the total resistance of valves Va and V4 is (indicated as R4) effectively high. But when condensers Ca and C4 are used in the circuit as indicated, the resistance R5 balances at a lower impedance value because each condenser presents low impedance to its particular half cycle of alternating current, i. e., C: for one-half cycle and C4 for the other halfcycle, and higher applied voltages cause the valve impedance of V3 and V4 to decrease.

The advantages in using C5 and C4 may be readily apparent in that all signal oscillations must flow through the resistor R3, the lower impedance thereof preventing excessive dissipatlon of signal energy. Further, the effectiveness of the valves V3 and V4 in discriminating between desired oscillations (signals) and undesired oscillations is improved by the use of the condensers Ca and C4.

When the signal voltages are impressed on the input terminals, they are unaffected by the Wheatstone bridge because of the existing unbalance of the bridge and are transmitted to the output terminals through resistances R2 and R3. The reason that the bridge is unbalanced is that the signal voltages cannot pass through the tubes V and V1 because the tubes are blocked or kept open by the biasing voltage. However, when disturbing voltages, which are of a higher amplitude than the voltage which keeps tubes V and V1 open, are impressed onthe input terminals, the bridge becomes balanced because these voltages render the tubes V and V1 effective conductors and the resistance represented by R4 balances the variable resistance R: and no current flows to the output. When a combined wave including signals and disturbing voltages is present, there is an output from the bridge to the primary P4 of transformer T4 which is substantially proportional to the percentage of signal in the combined wave. Of course, this also holds when there are no disturbing voltages present. This proportion occurs because as the amplitude of the combined wave increases. the bridge becomes more nearly balanced.

In Fig. 4, I and 2 represent the input terminals of a receiving system and may be connected to antenna and ground or to any other source of carrier wave signals. The terminals are connected to a primary P1 of the transformer T1 which is coupled to the tuned circuit S1 VC. Radio frequency currents are detected by the tube V1 and the output of tube V1 is coupled to the audio frequency amplifier V: by means of the transformer T2. The output of the tube V: is coupled to an intermediate circuit in which is contained the balancing network or Wheatstone bridge arrangement for preventing the disturbing voltages from being transmitted to the push-pull amplifying tubes V5 and V5 by means of the transformer T4.

The Wheatstone bridge arrangement comprises, as in Fig. 3, the fixed resistances R1 and R2 which are equal and comprise one arm of the bridge, the adjustable resistance R3 and the twoelement tubes V5 and V4 with a resistance R5 connected between them which comprise the other arm or balancing arm of the bridge. The resistance R5 is adjusted to equal the total resistance of the tubes when they are conducting so that the bridge becomes balanced and no current fiows to the primary P4 of transformer T4. the values of R1 and R2 are generally of the order of 100,000 ohms each and R3 is approximately In practice,

2000 ohms. The valve resistance of V3 and V4 (indicated as R4) may be approximately 2000 ohms when the valves are conducting and current fiows. Therefore, the total load across the secondary S3 will be less than 4000 ohms when undesired oscillations are present (tubes V3 and V4 conducting) but will be approximately 200,000 ohms when signal only is present (V3 and V4 not conducting). The secondary S3 is designed to operate into a load of 200,000 ohms or more and therefore is very inefficient in working into a 4000 ohm load which is the case when undesired 0scillations are present and therefore the undesired oscillations will be substantially reduced by this poor and inefficient transfer and thereby enhances the operation of the bridge. The effect, I have chosen to call the load effect due to the bridge. A biasing voltage is applied to the tubes V3 and V4 through the resistance R5 which is comparable with the peak signal voltage thereby blocking the tubes for signal voltages and unbalancing the bridge as will be discussed more fully hereinafter. Condensers C3 and C4 are provided across resistance R5 and function as in Fig. 3. The output of the push-pull tubes is coupledto the output terminals 3-4 by means of transformer T5. A circuit is coupled in parallel with the output of the tubes V5 and V5 containing the primary of transformer T6 and blocking condensers C6. The secondary of this transformer is connected to the grid of a rectifying tube V7 and to the negative terminal of the time circuit R'C in the grid-cathode circuit of the tube-V1. The cathode of the tube V1 is connected to an intermediate point on the resistance R'.- The positive terminal of the time circuit RC is connected to the plate of tube V1 through another time circuit RC. The output of the rectifierv V7 is coupled to a direct current amplifying tube Va by means of the time circuit RC. A filter comprising a choke and condenser C7 is provided to prevent any sudden surges being impressed on the circuit RC. The amplifying tube Va is supplied with plate potential from the battery B2, and a resistance R8 is shuntedacross the anode and cathode of the tube. Plate current from the tube Va is caused to flow through the resistance R8, producing a voltage drop therein, as indicated by the positive and negative signs, and the negative terminal of the resistance R8 is connected to one end of the resistance R5, while the positive end is connected to the other endof the resistance R5 through a battery B1 which provides a zero shunt for the output circuit with no load present, that is, when normal plate current is flowing through the resistance Re to produce a voltage drop, an equal voltage is provided by the battery B1 in the opposite direction, thereby preventing current flow and producing no voltage drop through the resistance R5 thus preventing bias voltages from being applied to the tubes V3 and V4 in the absence of signal. However, when the plate current increases to a value greater than normal, it overcomes the voltage of the battery B1, a current flows and a voltage drop is produced in the resistance R5 corresponding to the increment of plate current. a

In shunt with the time circuit R'C' are provided a rectifier D of any suitable half-Wave type and a source of uni-directional voltage E in series with the rectifier, and in the present instance, the negative terminal of source E is connected to the input terminal of the rectifier thereby preventing the rectifier from conducting until a positive voltage greater than that of source isalmpressed on. the rectifier. The positive terminalof E isconnectedto the positive terminal ofgRfCf. The-voltage of the source E is selectedto be equal to the voltageproduced across RjC' fonthemaximum signal for full normal outtheavoltage :01 'E, the rectifier will conduct due to the-positivegterminal of 'E being connected to the positive; terminal of R'C' and a voltage will be produced across D which is opposite and equal to the-differencebetween the high shock voltage andathe maximum voltageof E thereby reducing thegvoltageacross R'C' to the value required for maximum signal for'full normal output.

Another feature, of the rectifier D and source E whenapplied to the system of Fig. sis that the time constant of the time circuit R'C is reduced thereby-preventing the voltage thereacross from rlsingtabove; a: predetermined value which is the limiting value necessary for the operation of tube V2, which operation will be explained more fully hereinafter. Hence it will be seen that the effectspf shock voltages or of high amplitude voltagesofedisturbing carrierswill be substantially eliminated.

The reduction of the time circuitR'C' for certain vvoltagerangesmaybe accomplished in other waysrthan. thatshown as for example by reversing; elements D and E with respect to each other or with. respect to R'C.

The purpose. of the system including the tubes V7 and. Va is to provide a bias on tubes V3 and V4 across resistanceR5 which will correspond closely to the. envelope of the audio frequency signals and to prevent the biasing of tubes V3 and V4 when there are no signals or carrier present. Considering a hypothetical condition in which the tube V7 may be energized from a constant potential source instead of. being energized from the resistance R, as illustrated in Fig. 4 and the sourcebeing arranged so that the tube V7 rectifies energy from the secondary of the transformer T6; it is obvious that audio frequency signals appearing at the transformer T4 will be transferred through the tubes V5 and V6 and transformer T6 and will produce uni-directional voltages across resistance R. inthe plate circuit of the tube V7 which are substantially proportional to the audio frequency voltages. The voltages developed across the resistance R are amplified by the tube Va and appear across the resistance R8 in the plate circuit of the tube. After being passed through the zero shunt system B1, Ra, these. voltages are applied to the resistance R5 to bias the tubes V3 and V4. Accordingly, the DC voltages across R5 will correspond to the envelope of the audio frequency signal across transformer T4. Therefore, if no provision be made to prevent undesired oscillations from providing a bias across the resistance R5 they may produce sufficient bias across it to keepthe output arm of the bridge unbalanced with respect to the input arm'even for the peak voltages of the disturbing oscillations, thereby permitting them to be transferred to the speaker. Using asa-basis the fact that the audio frequency signal associated with agiven carrier cannot be "greaterin value-than that correspondingto modulation, resistance R is provided in the oath ode circuit of the signal detector V1 for supplying energizing voltages for the tube V7 in accordance with the carrier. The resistance R' provides a D. C. voltage across its terminals, as explained hereinbef ore, which is proportional to the carrier voltage onlyand is. unaffected by audio frequency currents. The voltage across the resistance R is dividedby meansof a tap, a portion of the voltage being transferred to the grid-filament circuit of the detector tube V7 to provide a grid bias on the tube andthe remaining larger portion being transferred to the plate-filament circuit to provide the necessary plate potential on the tube. The, tap on the resistance R is so adjusted that the normal grid and plate voltages applied to the detector tube V7 are of a value which best adaptsv the tube to rectification. From this arrangement, it will be apparent that when no carrier wave is, arriving at the detector tube V1 but only undesired oscillations, such as atmospheric static and the like, in the form of a buzz or other noises, the undesired oscillations will-be transferred to transformer T3 and a certain portion thereof may appear in the output of transformer T4 which, in turn, will be transferred to the out put terminals of the transformer Te. Obviously, the amount of energy in the plate circuit of the detector tube V7 is very limited because of the absence of the carrier. Therefore, in the absence of the carrier at the tube V1, substantially no energy will be transferred from V7 to V8 and to resistance R5 to bias the tubes V3 and V4. By reason of this action due to the absence of the carrier, substantially no undesired oscillations will appear at the speakeroutput terminals. Also,

for the same reason, when the carrier is present at the input terminals I and 2, but is not modulated, a certain amount of undesired oscillations may leak through the system and pass the valves V3 and V4, but the amount of bias is limited by the amount of current flowing through resistance R in the cathode circuit of the tube V1, so that the entire system will not respond to severe disturbing oscillations as it might if there were no limit, as is provided by the arrangement of tubes V7 andgVa.

The beginning of the operation of the bridge in the circuit of Fig. 4 may be better understood from the following:1n the original or normal condition of the complete system, there is no bias on valves V3 and V4 and, therefore, the bridge is balanced. Signal oscillations and undesired oscillations alike will be balanced out by the bridge.

The very first cycle of signal oscillations is balanced out in the bridge and does not produce any output in transformer T4. However, the positive half cycle of the signal flowing through V3, and through Ca and the upper portion of R5 will g'encrate a small negative bias on. the plate of V- (See Fig. 1 anddescription thereof.) Similarly, the negative half cycle will generate a small negative bias on the plate of V4. Valves V3 and V; are now partially biased so that in the next succeeding cycle, a portion of the signal goes to the output transformer T4 due to the partial unbalance of the bridge by the small negative bias on V3 and V4, and provides a normal bias. through the biasing system across R8 of tube V8, as explained hereinbefore, which builds up slowly and gradually because of time lag in the system due to filters and time circuits until the full strength of signals and bias is produced.

For the first cycle of undesired oscillations such asatmospheric. static. and the like. the initial function is the same as for signal oscillations except that by the time the first cycle of the unde sired or static oscillations (which are of a damped nature and relatively short duration as compared to signal oscillations) has built up a voltage across Rs in the output of tube Va, the static or undesired oscillation wave train has died out in the bridge and the small over-bias produced by the first cycle becomes ineffective to sustain any bias from RB.

If continuous undesired oscillations are present, a limit is provided by circuit R'C'-DE where they are in effect short-circuited and prevented from energizing tube V-: thereby preventing generation of excessive voltages at R and preventing a sustained unbalance of the bridge circuit.

From the above description, together with Fig. 4, it will be apparent that the circuit of my invention provides a system which will automatically prevent undesired oscillations from passing therethrough and prevent their being reproduced in the loud speaker regardless of whether there are signals present or not. It also provides an automatic bias on the tubes in the balancing network or bridge which varies in accordance with the amplitude or strength of the incoming signal voltages to maintain the network or bridge circuit unbalanced with respect to said signal oscillations so that they may be transferred therethrough to the transformer T4 and through the tubes V5 and V6 to the loud speaker terminals and which causes the network to become balanced with respect to the disturbing or undesired oscillations (such as static, line noises, etc.) thereby substantially eliminating any possibility of their being transferred to and through the transformer T4 and so on to the loud speaker.

The remaining elements of the system which have not been pointed out in detail are elements generally present in any receiving system and function in the usual manner.

The system of Fig. 4 may be susceptible to various modifications. It may be applied to radio frequency systems as well as to the audio frequency system which I have illustrated. The circuits would not be materially different and only the operating values of the essential elements would have to be changed. The circuit including tubes V7 and VB may be omitted and the bias for tubes V3 and V4 may be provided directly from the carrier voltage by means of the time circuit R'C' without departing from the principles disclosed. The bias thus derived may be slightly in excess of that required but it would take care of fading of the carrier wave.

While I have shown only two modifications of my invention for the purposes of illustration and description, other changes and modifications therein may be apparent to those skilled in the art without departing from. the scope of the invention and I, therefore, desire to be limited only by the scope of theappended claims.

I claim:

1. A system for reducing the effects of disturbing oscillations on signal oscillations comprising an input circuit, an output circuit and an auxiliary circuit associated with said input and output circuits including a pair of thermionic discharge devices normally biased to be rendered non-conductive to said signal oscillations and conductive to said disturbing oscillations thereby causing said signal oscillations to be transferred from the input circuit to the output circuit while the disturbing oscillations are blocked in said auxiliary circuit, and means connected to said output circuit for deriving a uni-directional voltage which varies in accordance with the amplitudes of the signal oscillations for biasing said discharge devices whereby said devices are always rendered non-conductive to said signal oscillations.

2. A system in accordance with claim 1 in which said voltage deriving means comp-rises a rectifying device for rectifying a portion of the signal oscillations and an impedance network coupling the output of the rectifying device to the input of said pair of thermionic discharge devices.

3. A system in accordance with claim 1 in which said voltage deriving means comprises a rectifying device for rectifying a portion of the signal currents and a time circuit comprising a resistance and capacity in parallel connected between the output of the rectifying device and the input of said pair of thermionic discharge. devices whereby the current from the rectifying device produces said biasing voltage which is applied to said discharge devices, and a filter in the output of said rectifying device for preventing sudden surges of current being appliedto said time circuit.

4. In a receiving system, means for reducing the effects of disturbing oscillations on signal oscillations comprising a normally unbalanced Wheatstone bridge connected between the input and output circuits of said system to pass said signal oscillations therethrough, one arm of said bridge comprising a fixed resistance and another resistance and another arm comprising a second fixed resistance equal to said first fixed resistance and a pair of thermionic discharge devices normally rendered non-conductive to signal oscillations, but conductive to the disturbing oscillations, the combined resistance of said'devices, when conducting, being balanced by said other resistance to balance the bridge, whereby the disturbing oscillations are rendered inefiec-= tive on said output circuit, and means for maintaining said discharge devices non-conductive to said signal oscillations in accordance with the amplitudes of said signal oscillations.

5. In a carrier wave receiving system, means for reducing the effects of disturbing oscillations on signal oscillations, comprising a balancing impedance network into which both of said oscillations pass, means for deriving a uni-directional voltage from the system which varies inaccordance with the envelope of the signal oscillations, means for deriving a second voltage from the system which varies in accordance with the carrier, means for causing said second derived voltage to limit the first derived voltage to a predetermined extent, and means for applying the limited voltage to said impedance network whereby said network is unbalanced for the signal oscillations to permit them to pass therethrough.

6. In a carrier wave receiving system comprising a stage of carrier frequency amplification, a detector stage, and a stage of audio frequency amplification, means for reducing the effects of disturbing oscillations on signal oscillations comprising a normally unbalanced impedance network between the input and output of said system whereby said signal oscillations may pass through said network, means for rectifying a portion of said signal oscillations whereby a unidirectional voltage is produced, means for deriving a plurality of uni-directional voltages from the carrier wave for energizing said rectifying means in accordance with the carrier to limit the voltage from said rectifying means, and means for applying said limited voltage to said network, wherebysaid network is maintained balanced for the disturbing oscillations and unbalanced for the signal oscillations.

7. In a receiving system, means for reducing the effects of disturbing oscillations on signal oscillations comprising a balancing network including a plurality of unilateral impedance devices, a time circuit associated with said unilateral impedance devices whereby a biasing voltage is built up to render said unilateral impedance devices non-conductive for said signal oscillations thereby causing said network to become unbalanced to pass said signal oscillations therethrough, means for deriving a uni-directional voltage from said signal oscillations and means for applying said derived voltage to said network to maintain said unbalance, and means connected between said balancing network and said last-mentioned means for preventing sudden surges of voltage affecting said network.

8. In a receiving system, means for reducing the effects of disturbing oscillations on signal oscillations comprising a balancing impedance network including a plurality of unilateral impedance devices, a time circuit associated with said unilateral impedance devices comprising a resistance connected between said unilateral devices and a pair of condensers, each of which is connected to a portion of said resistance whereby a biasing voltage is built up to render said devices non-conductive for said signal oscillations thereby causing said network to become unbalanced to pass said signal oscillations therethrough, means for deriving a. uni-directional voltage from said signal oscillations, and means for applying said derived voltage to said network to maintain said network unbalanced for said signal oscillations.

9. In a receiving system, means for reducing theefiects of disturbing oscillations on signal oscillations comprising a balancing network, normally unbalanced to cause said signal oscillations to pass therethrough, means for amplifying said signal oscillations from the output of said network, means for deriving a uni-directional voltage from said amplified signal oscillations, and

meansfor applying said derived voltage to said network whereby said network is maintainedunbalanced for said signal oscillations in accordance with their amplitudes.

10. In a-radio receiving system, a vacuum tube having a grid and a cathode, a time circuit comprising a condenser shunted by a resistor interposed in series between said grid and said cathode, and means for preventing the building up of an excess charge on said time circuit due to excessively high voltages which may be impressed on the input of said system, said means comprising an asymmetrical device provided with a suitable biasing voltage and connected in shunt with said time circuit.

11. In a receiving system, means for reducing the effects of disturbing oscillations on signal oscillations comprising a balancing impedance network including a plurality of uni-lateral impedance devices, and a time circuit associated with said uni-lateral impedance devices comprising a resistance connected between said uni-laterai devices and a pair of condensers, each of which is connected to a portion of said resistance whereby a biasing voltage is built up to render said devices non-conductive for said signal oscillations thereby causing said network to become unbalanced to pass said signal oscillations therethrough.

12. In a receiving system, a balancing device comprising a thermionic discharge device, said thermionic device being normally unbiased to ef- 13,.In a receiving system, a balancing device;

comprising a pair of thermionic discharge devices, said thermionic devices being normally unbiased to effect a balance of said balancing device, means for deriving a biasing potential for said thermionic devices from the output of saidbalancing device to unbalance the same for currents of predetermined amplitude, and means for causing the initial cycle of said currents to set up a biasing potential on said thermionic devices to unbalance said balancing device and initiate operation of said first mentioned means.

14. In an electrical wave signaling system, a signal transfer stage comprising a Wheatstone bridge including a pair of thermionic discharge devices in one arm thereof, means for supplying incoming signals to said signal transfer stage, means for deriving a unidirectional voltage from selected incoming signals having a desired amplitude, said voltage varying in accordance with the amplitudes of said selected signals, and means for applying said unidirectional voltage to said discharge devices in such direction that the transfereffectiveness of said signal transfer stage increases as said selected signal increases.

15. In an electrical wave signaling system, a signal transfer stage comprising a Wheatstone bridge including a pair of thermionic discharge devices having a resistance connected between them in one arm of said bridge, means for supplying incoming signals to said signal transfer stage, means for deriving a unidirectional current from selected incoming signals having a desired amplitude, said current varying in accordance with the amplitudes of said selected signals, means for passing said current through,

frequencies, means for controlling the transfer ef-,

fectiveness of said stage, means for deriving control energy from said waves of certain frequencies and for applying said energy to said control means, and for deriving control energy from waves of another frequency and for applying said energy to said control means, whereby the transfer effectiveness of said transfer stage is controlled in accordance with the amplitude of said waves.

17. In a modulated carrier wave receiving system, a demodulator, a transfer stage for the signal waves produced by demodulation, means for controlling the transfer effectiveness of said stage, means for deriving control energy from said signal waves and for applying said energy tosaid 10 controlling the transfer effectiveness of said stage, means for deriving unidirectional control energy from said signal Waves and for applying said energy to said control means, and means for deriving unidirectional control energy from the carrier wave and for applying said energy to said control means, whereby the transfer effectiveness of said transfer stage is controlled in accordance with the amplitude of said Waves.

DAVID G. MCCAA. 

